ANALYSIS OF THE ROLES OF HISTONE DEMETHYLASES IN DROSOPHILA MELANOGASTER MALE GERM CELL MAINTENANCE AND DIFFERENTIATION

Adult stem cells reside in microenvironments called niches, where they are regulated by both extrinsic cues such as signaling from neighboring cells and intrinsic factors such as chromatin structure. Here we report that in the Drosophila testis niche, an H3K27me3-specific histone demethylase encoded by ubiquitously transcribed tetratricopeptiderepeat gene on the X chromosome (dUTX) maintains active transcription of Suppressor of cytokine signaling 36E (Socs36E) gene by removing the repressive H3K27me3 modification near its transcription start site. Socs36E encodes an inhibitor of the Janus kinase signal transducer and activator of transcription (JAK-STAT) signaling pathway. While much is known about the niche-to-stem cell signaling, such as the JAK-STAT signaling critical for stem cell identity and activity, our results reveal that stem cells send feedback to niche cells to maintain the proper gene expression and architecture of the niche. We found that dUTX acts in cyst stem cells to maintain hub cell identity through activating Socs36E transcription and preventing hyperactivation of the JAK-STAT signaling. dUTX also acts in germline stem cells to maintain hub structure through regulating DE-Cadherin levels. In addition to the role of dUTX in the testis niche we report that in the Drosophila testis, an H3K4me3-specific histone demethylase encoded by little imaginal discs (lid) maintains germline stem cell self-renewal and prevents premature differentiation. Lid is required cell-autonomously in germ cells for proper expression of the Stat92E transcription factor, the downstream effector of JAK-STAT signaling pathway. Our findings support a germ cell autonomous role for the JAK-STAT pathway in maintaining germline stem cells and place Lid as an upstream regulator of this pathway. Our findings provide new insights into the biological functions of histone demethylases in vivo and shed light on the interaction between epigenetic mechanisms and signaling pathways in regulating stem cell activities. In addition to our studies in the testis niche we report a role for dUTX in spermatocyte maturation. Our findings suggest that dUTX cooperates with the testis-specific homologs of TBP-associated factor (tTAFs) to sequester repressive factors to the nucleolar regions of spermatocytes and allow the transcription of terminal differentiation genes. The readers of this thesis are: Dr. Allan Spradling, Dr. Xin Chen, Dr. Mark Van Doren, and Dr. Daniela Drummond-Barbosa

Epigenetic regulator Lid maintains germline stem cells through regulating JAK-STAT signaling pathway activity

Signaling pathways and epigenetic mechanisms have both been shown to play essential roles in regulating stem cell activity. While the role of either mechanism in this regulation is well established in multiple stem cell lineages, how the two mechanisms interact to regulate stem cell activity is not as well understood. Here we report that in the Drosophila testis, an H3K4me3-specific histone demethylase encoded by little imaginal discs (lid) maintains germline stem cell (GSC) mitotic index and prevents GSC premature differentiation. Lid is required in germ cells for proper expression of the Stat92E transcription factor, the downstream effector of the Janus kinase signal transducer and activator of transcription (JAK-STAT) signaling pathway. Our findings support a germ cell autonomous role for the JAK-STAT pathway in maintaining GSCs and place Lid as an upstream regulator of this pathway. Our study provides new insights into the biological functions of a histone demethylase in vivo and sheds light on the interaction between epigenetic mechanisms and signaling pathways in regulating stem cell activities